Printing telegraph system



3 Sheets-Sheet 1 1940- w. B. BLANTON I rmn'rme TELEGRAPH sYs'n-m 7 Filedlarch 29, 1938 U 0 ul' l2 CALLI NG TRUNKS INVENTOR ORNEY W. B. BLAN TONv BYZAQar-OIN Patented Dec. 31, 1940 PATENT OFFICE PRINTING TELEGRAPH SYSTEM William B. Blanton, Merrick, N. Y., assignor to The Western'UnionTelegraph Company, New York, N. Y., a corporation of New YorkApplication March 29, 1938, Serial N5. 198,633

22 Claims.

This invention relates to printing telegraph systems, and moreparticularly to multi-oflice systems embodying acentral station-and aplurality of branch ofllces or stations.

The primary object of the invention is to decrease the number ofchannels or circuits required between the branchoflicesand the mainoffice or central station of a multi-ofilce system, or to increase thetelegraph facilities between outlying branch omces and the centralstation or main oflice.

A telegraph system to which the invention is applicable would be onewhere a considerable number of branch ofilces or stations are located ina relatively small area remote from the central 1 station, or so locatedthat the installation or maintenance of connecting circuits is diflicultor expensive, as for example where a group of branch stations arelocated on the opposite side of a river or a bay from the centralstation so that a connecting cable is required. In order to decrease thesize of the cable required or to provide for increased facilities as thenumber of branch omces increases, in accordance with the 2 invention,switching means would be provided in connection with the signalingchannels from the central station arranged to connect the signalingchannels to a wanted branch station, or in the case of a call from abranch station, to connect the calling station to an idle one of thesignalin channels to the central station. In. this manner acomparatively large number of branch stations may be operated over asmall number of common signaling channels to the central station.

It is an object of the invention to provide a multi-ofilce telegraphsystem having a switching center for controlling the channels betweentherespective ofiices, which switching center may be remote from thecentral oilice and all or all but 'one, of the branch oflices. Since theprinters in the printing telegraph system embodying the invention may beused by subscribers or patrons as well as in branch oflices of thetelegraph company, the term branch office is intended to cover asubscriber's or patron's oifice.

Another object of the invention is to provide a multi-omce telegraphsystem having switching means for connecting the central oflice to awanted branch oflice and vice versa in which some of the branch oflicelines are used only in calling from the central ofilce and others onlyin calling from branch ofllces.

Another object of the invention is to provide a multi-oillce system ofthe character described 55 adapted for central oflices having aconcentrator for selectively connecting operators printers with callingand called branch omces and preferably a concentrator having terminalsof direct lines to branch ofllces as well as terminals of branch oflicesconnected through the switching center. 7 Another object of theinvention is to provide a multi-omce system of the above characterhaving concentrator operators sets at the central oifice adapted to beconnected either to direct branch-office lines or switching centerchannels and to provide certain guard features to prevent the operatorfrom sending into switching center channels before connection-has beenmade to a remote branch office and for other purposes.

Another object of the invention is to provide a telegraph system havingselector switches to connect to wanted lines, the switches beingcontrolled by current impulses transmitted over the telegraph lines orcircuits, and in which the operativeness of the telegraphv transmitterdepends either upon the prior transmission of selective impulses forsetting the selector switch or upon the connection to telegraphreceiving apparatus.' This feature of the invention prevents aninadvertent attempt to transmit a message before the connection has beenextended to the wanted line or oflice.

Other objects and advantages of the invention will appear from thefollowing description of the system shown on the accompanying drawingswherein Fig. 1 is a schematic di-agramof the preferred embodiment of theinvention, and

Figs. 2 and 3 are diagrammatic views of the detailed circuits of thesystem shown in Fig. 1.

Referring toFig. '1, a typical system embodying the invention comprisesa central station or main office M, a plurality of branch oflices orpatrons offices A and B connected by direct line circuits In and Ii tothe main oflice, and other branch offices C, D, E and F adapted to beconnected to the main ofiice through the switching center S and branchoflice channels or trunks l2 and Hi. It will be apparent that by theprovision of selectively operable switches at the switching center S tocontrol the connection of a callingor called branch office to thechannels I! and [3, the number of such channels may be 50 considerablyless' than the number of branch offices since the latter are not incontinual operation. The invention is of particular value thereforewhere the installation or maintenance of the circuits i2 and I3 isdifiicult or expensive, 5s

by the growth of the system in the proximity of the branch ofiices C, D,E and F, since the additional ofilces may be placed in service withoutthe installation of additional trunk circuits to the main ofiice.

As shown, the trunk circuits l2 are employed in selecting a wantedbranch oflice from the main or central station and are designatedcalling trunks, whereas the trunk circuits ii are accessible to callingbranch oflices and are designated "answering trunks. The calling trunksl2 terminate at the switching center S in selectors s which arecontrolled from the central station or main oilice in order to connect awanted branch office. 0n the other hand, when one of the branch omces C,D, E or F has a message to send to the central station, the branchoflice operator transmits a signal as by depressing a key of the printerkeyboard whereupon one of the finder switches f at the switching centerconnects the branch ofllce to one of the answer trunks l3 to the mainoflice or central station M.

After a connection is established between one of the branch oilices C,D, E or F, and the main oiiice M over either a calling trunk or ananswering trimk, two-way communication may be had between the main andbranch ofllces. On the other hand, if the main oflice places a call fora branch ofilce which is already connected to the main office or hasinitiated a call thereto, a busy signal is transmitted from theswitching center .be employed to connect the operators printers Ii atthe main omceto any calling or called branch oflice. As indicated, theconcentrator switchboard may include terminals of both direct lines Inand II- to branch omces and channels l2 and I3 to the switching centerS. Certain of the operators printers at the main ofllce are providedwith a calling dial l1 and a key or switch l8 whereby the printer may beconnected to one of the calling trunks and impulses transmitted over thecalling trunk for controlling the selector switches s. In accordancewith another feature of the invention, the selection, control andintelligence signals, and in the case of an attempted call to a busybranch oflice, the busy signal, are transmitted over a single lineconductor. In accordance with a still further feature of the inventionprovision is made whereby the operator's printer [6 will not functionafter actuating the key I8 if ,an attempt is made to transmit messagesignals over a calling trunk l2 before th. dial I! has been operated ora branch office has been connected by the associated selector switch S.

For abetter understanding of the present in-' vention, reference may behad to Figs. 2 and 3 illustrating the detailed circuits of the system,shown in Fig. 1. IngFig. 2 is shown the operthrough the switchingcenter, together with two oi the branch oflices A and 3 connected bydirect line circuits to the main oflice M.

The apparatus at the main office M includes a concentrator orswitchboard for connecting operators printers to the branch omce linesof the type disclosed in the patent to Drake and Blanton, No. 1,804,327dated May 5, 1931. Reference may be had to said prior patent for acomplete description of the main office equipment, certain features ofwhich have been omitted for the sake of simplicity. In general, theconcentrator comprises manual switching equipment such as plugs andjacks for connecting any printer to any branchoflice line to answercalls irombranch oflices and to originate calls to the branch offlces.

4 tion, the call lamp l9 being lighted when a call is initiated to themain oflice from a branch ofllce, as for example by the branch oihceoperator momentarily interrupting the line circuit.

The line circuits are normally connected to positive battery at the mainofiice until an operator plugs in a printer to originate or answer acall,

whereupon the polarity of the line circuit is reversed.

The printer lishown in Fig. 2 is arranged to be used in connection withtransmission to or from the branch ofllces A and B (Fig. 3) connected bythe direct line circuits l0 and H to the main oflice M and also fortransmission of messages through the switching center S to and from theremote branch oilices, such as C and D (Fig. 2). The calling trunk I2shown in Fig. 2 is representative of the several calling trunksprovided, the number of which depends upon the peak message load. Sinceeach of the calling trunks is similar to the trunk l2, and the apparatusassociated with each of the answering trunks I3 is also similar to thatshown, a description of the operation of one calling trunk and oneanswering trunk will suflice.

Call from main oIfice to branch. ojfice A polarized relay 24 isconnected in series relation with the calling trunk l2 to respond tocurrent impulses for controlling the selector 8 transmitted over saidtrunk. The armature of said relay is provided with mechanical bias asshown, 'or with electrical bias tending to hold said armature againstits right hand contact.

The armature of relay 2|, however, is held in engagement with its lefthand contact by the current traversing the calling trunk l2 when idleand thereby energizes associated relay 25 during this period. Thecircuit of relay 24 may be traced from positive battery at the mainoffice through the right hand break contacts of the key switch l8,conductor l2, the winding of relay 24, .the make-before-break contactsassociated with the middle right hand armature ofrelay 26, resistance21, the inner right hand armature and backcontact of relay 28 and arectifier 29 to ground. The rectifier 29 is poled to pass the linecurrent flowing when the trunk I2 is connected to posi tive battery atthe main oflice.

when the operator atthe main oflice desires to initiate a call throughtheswitching center S to one of the branch offices, for example branchofflce D, the key or switch I8 is operated, it being assumed that theprinter I6 is idle and the plug 2.2. associated therewith is removedfrom the of key IS, the above-described circuit of relay 24 isinterrupted at the break contacts of said-key and a new circuit isestablished through'the right hand make contacts of 'saidke'y, theoff-normal contacts of the dial H, the contacts and printer magnet ofthe printer l6 and resistance 2| to negative battery. As a result of thereversal of polarity, the flow of current in the conductor l2 andwinding of relay 24 is decreased to a relatively small value by therectifier 29 and the armature of relay 24 is actuated into engagementwith its right hand contact by the retractile spring or bias of saidrelay;

Upon the release operation of relay 24 the circuit of relay 25 is brokenand a circuit is closed through the right hand contact of relay 24 forenergizing relay 3|, relays 25 and 3! being both 'of the slow-to-releasetype. The apparatus at the switching center is now in condition foroperation in response to the transmission of selector impulses from thedial IT at the main office.

It will be noted that a different switching 0D- eration, l. e.,operation of the key l8, precedes the dialing of a call through theswitching center whereas in the'case of calls to the branch -oiiices 'Aand B, the operator plugs the connection into a jack representing thewanted office. In the latter instance, the operator may commencetransmission immediately or upon the. reception of GA (go ahead) fromthe branch ofiice. In order to prevent the operator from proceeding inthis manner inadvertently inthe case of a call through the switchingstation, the line circuit is opened in efiect by the rectifier 29 untilafter the number of the wanted station has been dialed. The printer I6is of the start-stop type, operating in response to rest and mark ngcurrent impulses and start and spacing impulses of zero current. Thusthe printer runs idle while the line current is zero and the operatorcannot send until normal line current corresponding to the normal'restcondition is established.

Any suitable form of selector switch may be employed in the switchingcenter. For the purpose of explaining the invention, a conventionaltwo-motion step by-step selector switch is shown having an auxiliaryminor switch 33'- controlled by a stepping magnet 34 and release magnet35. The selector switch comprises vertical and rotary stepping magnets36 and 31, respectively, and a release magnet 38adapted when energizedto permit the restoration of the arms or wipers of the selector switchtonormal. The upper switch wiper 39 of the selector is adapted to extendthe calling trunk I2 to the line extending to the called branch ofliceand the lower wiper 40 of the selector is arranged to test the busy oridle condition of the called oilice to guard against the seizure of abusy line. The stationary contacts of the respective selector switchesassociated with the several calling trunks [2 are multipled together,and in case the called cfiice has already been selected by anotheroperator or a call initiated from said office, the contacts engaged bythe test wipers of the other selectors have ground potential thereonwhich serves to prevent the connection to the busy ofiice in a mannerthat will be described.

The operation of the selector in response to the actuation of thecalling dial ll is as follows:

above, a circuit is closed through the armature when relay 25 becomesdeenergized as described,

and back contact of saidrelay for energizing the stepping magnet 34 ofthe minor switch 33, whereupon the movable switch arm of said switch isstepped into engagement with the second contact thereof. When theoperator dials the first digit of the wanted branch oflice D, theoff-normal contacts of the dial are opened and the dial-v ing contactsare closed a number of times cor-' responding to the number dialed. Theclosure of the dialing contacts of the dial 11 connects positive batteryto the calling trunk l2 which at this time is disconnected from negativebattery by reason of the opening of the oil-normal contacts of saiddial, each current impulse from the calling dial ll thus momentarilyenergizing the polar relay 24 and actuating the armature thereofmomentarily into engagement 'with its left hand contact. Relay 25 thusbecomes reenergized and again opens the circuit of the stepping magnet34 of the minor switch. However, since relay 25 is a slow-to-releaserelay, its armature remains attracted during the series of impulses fromthe calling dial "and these impulses are reproduced by the armature ofrelay 24 through" a circuit including the left hand contact ofsaidrelay,the switch arm of the minor switch 33 and the-vertical magnet 36 of theselector switch-f so that the wipers of said switch are actuated anumber of steps corresponding to a number 'of impulses dialed by theoperator. At the end of the first series of impulses the slow-to-rcleaserelay 25 becomes deenergized, reclosing the circuit of stepping magnetto step the wiper of the minor switch 33 to the-third contact thereof.Slow-to-release relay 3|, however, remains sufliciently energized tomaintain its armature attracted during thev entire dialing operation.

Theoperator now dials the second digit of the number of the calledoffice, whereupon the above operations are repeated except that theselective impulses are diverted through the minor switch 33 to therotary magnet 31 of the selector switch. In this manner the wipers 39and of the selector switch are actuated into engagement with theterminals corresponding to wanted oflice D. At the end of the secondseries of impulses slow-to-release relay 25 again becomes deener-' gizedand again closes the contact of the stepping magnet 34 of the minorswitch, whereupon the wiper thereof is actuated into engagement with itsfourthcontact.

Upon the operation of the minor switch as dc-, scribed, a circuit isclosed from positive battery through the winding of relay 25, the minorswitch 33 and the winding of relay 28 to ground, whereupon relays 25 and28 become energized.

Assuming that the wanted branch office is idle,

comes energized and relay 28 is sufiiciently energized to close itsinner' right hand armatur and preliminary make contact, whereupon theresistance 43 isshunted by the last-mentioned contact and a much largercurrent flows through the circuit. This increased flow of current causesrelay 28 to become fully'oper'ated whereupon the calling trunk I2 isconnected through the middle right hand armature of relay 26, the wiper39 of the selector 3 to the line 66 extending to the called branchoflice D. Likewise the relay 26, at

its left hand armature and front contact closes a shunt circuit throughthe rectifier 44 around the winding of polar relay 24. The rectifier 44is poled so as to oppose the how of current through this shunt circuitwhen positive potential is applied to the trunk l2 at the main omce, butto offer a relatively low-resistance shunt path around the winding ofrelay 24 under normal transmitting conditions when negative potential issupplied at the main office. The purpose of this rectifier is to improvethe transmission characteristics of the trunk circuit by removing theinductance of the winding of relay 24 from the circuit, while at thesame time not to interfere with the signaling and control functions ofthe system.

The line circuit 60 extending to the branch oflice D is normallyconnected through the makebefore-break contacts associated with the lefthand armature of relay 55, the winding of relay 56 and resistance 51 topositive battery. Relay 56 is thus normally energized, its circuitfurther including the contacts and printer magnet of the printer 6|, thewinding of polar relay62 and resistance 63. When a connection is made asdescribed above to the line circuit 60 through one of the selectorswitches and relay 55 becomes energized as described above, relay 56 ismaintained energized through the left hand armature and make contact ofrelay 55 to prevent initiating a false call to the apparatus'associatedwith the answering trunks l3. The connection to positive battery throughresistance 51, relay 56 and polar relay 62 maintains the contacts of thepolar relay 62 open. However, when negative battery is applied throughthe selector switch 3 to the line circuit 60 from the main omce, thecontacts of polar relay 62 are engaged and light the "call lamp 65. Inresponse to the call the branch office operator closes the switch 66shunting out the inductance of the polar relay 62, the switch beingarranged if desired to start the motor of the printer 6|. Alternatively,the driving motor of the printer if not running continuously may bestarted by the operation of relay 62. The operator at the branch ofliceDnow sends GA (go ahead) whereupon the main offlce operator is apprisedof the fact that the branch omce has answered and transmission proceedsin the usual manner. Since the contacts and operating magnets of theprinters l6 and 6| are in series, twoway communication may be had overthe trunk v|2 and branch ofllce line 60.

At the end of the exchange of business, the main ofllce operatorrestores the key l6 thereby disconnecting the trunk circuit l2 from theprinter and connecting the same to positive battery through the righthand break contacts of the key. The reversal of the current in the linecircuit as the result of the reversal of the polarity of the batteryconnected thereto at the main office causes the armature of polar relay24 to move against itsleft handcontact thereby interrupting the circuitof relay 3|. Relay 3| becomes deenergized and closes through itsarmature and back contact, and the off-normal contacts 4| and 42 of theselector switch and minor switch, respectively, circuits for energizingthe release magnets 38 and 25 of said switches, whereup n the switchesare restored to normal. When the wipers of the selector and minorswitches are restored to their normal positions,

; switch I as will be described hereinafter.

the off-normal contacts 4| and 42 are opened. 2

The restoration of the minor switch 33 also interrupts theabove-described circuit of relay 28 whereupon this relay becomesdeenergized and interrupts the circuit of relays 26 and 55 through itsleft hand armature and front contact. The circuit of relay 55 is alsointerrupted by the restoration of the test wiper 40 of the selectorswitch to normal. Relays 26 and 55 are thus deenergized so that allequipment and circuits at the main ofllce and the switching center arerestored to normal in readiness for use in establishing anotherconnection.

Upon the deenergization of relay 55, the branch office line circuit 60is reconnected through the make-before-break contacts associated withthe left hand armature of said relay to the positive battery at 'therelay 56. The polar relay 62 at branch oflice D is thus operated in sucha manthe selector switch s connected the calling trunk |2 to theterminals of said branch oifice. If the branch ofllce D had been busy,the lower bank contact engaged by the test wiper 40 would have been ator near ground potential. In the case of a previous call initiated fromthe main oflice through one of the other selectors s, the test bankcontact would have been grounded through the left hand armature of arelay corresponding to relay 28 and the winding and right hand innerarmature and front contact of the relay corresponding to relay 26. Inthe case of a previous call initiated from the branch oflice D, the bankcontact'would have been grounded at the finder The bank contact may also'be grounded by the busying key 5| in case a branch oflice circuit is tobe disconnected from service during testing or repairs being efl'ectedon the branch omce circuit.

When the selector switch ,3 is operated to connect to the branch officeD when the latter is busy, the ground potential on the test contactwhich is connected through the test wiper 40 and the left hand armatureand front contact of relay 28 to the test relay 26 does not operaterelay 26-since this relay is also connected to ground through theresistance 43. Relay 26 thus does not become energized in case anattempt is made to connect to a busy branch office and therefore thecalling trunk I2 is not connected through the middle right hand armatureand front contact of said relay to the switch wiper 39, but remainsconnected through the make-before-break contacts associated with saidrelay, the resistance 21, the right hand inner armature and frontcontact of relay 28 to the busy signal transmitter having interruptercontacts 46 connected to the front contact associated with the innerright hand armature of relay 28. The transmitting device 45 may be amotor driven commutator arranged to send signaling impulses of anydesired character to the printer IE to indicate that the desired branchoffice or patro'ns office is busy.. The transmitter may be runningcontinually or started if desired upon the closure of a circuit throughthe outer right hand armature and front contact of relay 28 and theouter right hand armature and back contact of relay 21 as shown.

- Thus, if an attempt is made to connect to a bu y branch oflice, theconnection is not effected but the calling operator is signaled that thebranch office dialed is busy. v

If the operator restores the key I8, the switching center equipment isrestored to normal in the same manner as in the case of a completed calldescribed. However, if the operator does notrestore the key I8 but waitsuntil the wanted branch ofiice is idle, the connection will beautomatically effected between the calling trunk I2 and the branchofiice when the latter becomes idle. The idle'condition of the branchoffice will be indicated by the removal of ground potential from thelower bank contact associated with the test wiper40 whereupon test relay26 will be energized in series relation with the relay 55 as describedabove in the case of a call to an idle branch ofiice. The energizationof relay 26 .will interrupt the busy signaling circuit from the busysignal transmitter 45 and will connect the calling trunk I2 through theswitch wiper 39 to the called, branch ofilce. Subsequent operations ofthe system will be the same as described above in connection with acompleted call to an idle line.

Call initiated from a branch ofllce Assuming that the driving motor ofthe printer at the branch ofiice D is running continually or hasbeenstarted by the operation of a conventional manual starting switch, thebranch office operator initiates a call to the main omce by pressing anykey on the printer, thereby momentarily opening the line circuit 60entending to the switching center and interrupting. the

current through series relay 56. As explained above, relay 56 isnormally energized when the of printer 6|, the winding of relay 62andresistance 63'to ground at the branch oflice. When relay 56 becomesdeenergized as described above, a short-circuit around the winding ofsaid.

relay is closed through the left hand armature andback contact of relay55. Thus relay 66 remains deenergized until the circuit has beenrestored and the short-circuit opened by the operation of relay 55. 7Upon thedeenergization of relay 56 as described, a start circuit isclosed from ground through the right hand armature and back contact ofsaid relay, the right hand; break contacts of the key the break contactsof the trunk busying key I05, Fig. 3, the fourth right hand armature andbackcont'act of relay I06 and the winding of relay I01 tobatterywhereuponrelay I01 becomes energized. --The respective finder switches fare each associated with individual answering trunks I3 to the mainoflice and the foregoing description assumes that the first findrelay 56would be transferred from the fourth right handarmature and back contact.of relay I06 to the front contact associated with said armature throughthe break contacts of busying key 205 to the control equipmentassociated with 20I, 202, and 203 and the stepping magnet 204. Aplurality of finder switches are thus provided, one for each answeringtrunk, suflicient to take care of the maximumnumber of simultaneouscalls from the group of branch offices C, D, etc. Upon the operationof-relay I01 as described above, the left hand armature of said relayopens the circuit including thetrunk I3 to the main oflice to initiate acall to said ofl'ice. As shown, the trunk J 3 is connected through thewinding of polar relay I I0, the make-before-break contacts associatedwith the inner left hand armature of relay I06, resistance III and theleft hand armature and back contact of relay I01, to ground.

The trunk I3 terminates at. the main ofiic'e in signaling and controlequipment of any suitable character. equipment comprises relays 15, I6and I1, arranged to control the call and busy lamps I9 and 20, togetherwith interrupter contacts I9 arranged as shown in the above mentionedprior patent to Drake and Blanton. The trunk circuit is normallyconnected through the makebefore-break contacts associated with themiddle As shown in Fig. 2, the control.

armature of relay 15, the winding of relay 'lland the resistance 18 topositive battery. The I I described circuit normally maintains relay I1energized and because of the connection to posiat the switching centerto maintain, the a'rma:

ture thereof in engagement with its left hand contact.

Upon the momentary interruption of the trunk circuit as described, relay11 becomes .deenergized and closes through its right hand armature backcontact of relay 11 a short circuit around its own winding so that therelay remains deenergized upon the reclosure-of the line circuit.

The deenergization of relay 11 also closes through its left handarmature,..and back con and back contact and the upper armature and tactthe circuit of.call lamp I9, whereupon this lamp becomes lighted toindicate'to the, op-

erator that ,a call has been received on the trunk I3 from a remotebranch oflice.

When the operator plugs aprinter such-as the through the lower Windingof. relay I6 to-the corresponding jack I5, the plug 22, the left handbreak contacts of the key- I8, the contacts and printer magnet of theprinter I6 and resistance 2| tonegative battery, whereupon the polarityI5 and the lower interrupter contact 19 a lockcircuit for said'relayincluding the upper in" terrupter contact 19. Theoperators printer's,the 'main office is now connected to the callinj circuit, but beforethis connection has been mad a .finder, switch I 'hasoperatedto connectcalling branch office' to this main oifice" line: cuitin a mannerwhichwill now be described The bank contacts associated with-the printerI6 intolthe jack I 5-associated with the trunk'circuit I3, the trunkcircuit H3 is extended tive battery operates the series polar relay IIO3 E ing circuit for relay I6 and-an-operating circuit 9 forrelay' I5.The energization of relay I5 at its .middle armature and front contactopens the above describedcircuit of relay 11," and closes.

the circuit for operating -the busy"- lamp '20..- The energization' ofrelay I5 further closes at its lower armature and front contact alocking .v

mally grounded by the relays 56 associated with the respective branch'ofiice circuits. When, however, a call is initiated from. one of thebranch ofiices as described above, ground potential is removed by relay56 from the bank contact in each of the finder switches, correspondingto the calling branch office. Upon the operation of relay I01, asdescribed above, a circuit is closed from positive battery to thestepping magnet of the first idle finder switch, for example, thestepping magnet I04 of the first finder switch and the interruptercontacts thereof, the outer right hand armature and front contact ofrelay I0I, the third right hand armature .and back contact of relay I00,wiper IM to ground potential, assuming that the wiper IOI is not alreadyin, engagement with the bank contact corresponding to the calling branchoiiice. In response to the energization of stepping magnet I04, theswitch wipers IOI, I02 and I03 are stepped until the wiper IOI reachesthe ungrounded contact individual to the calling office, at which timethe stepping magnet I04 becomes deenergized and the switch wipers remainin engagement with the bank contacts associated with the callingoflice.

Upon the energization of relay I01 as described above, a circuit is alsoclosed from positive battery through the stepping magnet I04 of thefinder switch, the outer right hand armature and front contact of relayI101, the inner right hand armature and front contact of said relay andthe winding of relay I06 to ground. However, as long as wiper IOI of thefinder switch is stepping over grounded contacts the winding of relayI06 is short circuited and the relay is not energized. However, as soonas the wiper 'IOI reaches the contact associated with the calling branchoifice which is not grounded, relay I00 becomes energized. The outerright hand armature and the front contact of relay I00 are adjusted toengage before any of the other contacts of said relay are made or brokenand a circuit is thus closed from battery through the winding of relayI01, the outer right handarmature and front contact of relay I00, the.inner right hand armature and back contact of relay] I0 and the lefthand armatureand front contact of relay I01 whereby the latter relay ismaintained energized in spite of the fact that this original circuit isbroken at the fourth right hand arinature and back contact of relay I00.The energization of relay I00 through its fourth right hand armature andfront contact. transfers the start circuit through the busying key I06to the control equipment associated with the second-finder switchthrough the break contacts of the second busying key 205. Hence thesecond I finder switch will be started to hunt for the next branchoffice that initiates a call through the switching center to the mainofiice M. This connection will be established in .the same manner asdescribedabove in connection with the call initiated in the branchofllce D through the first finder switch. The energization of relay-I00also change of business between the respective omces,

' the operator at the main omce will disconnect her .cord circuit bywithdrawing the plug from the interrupts at its third right handarmature and back contact the above described circuit between thewiper mof the finder switch and the step- I L'ping magnet I04, and at the frontcontact associated with said armature connects ground potenf tiple withwhich said wiper isengaged is grounded tial to the wiper I" so that thebank contact mul and will not be selected by another finder switch.

The energization of relay through its second right hand armature andfront contact, and the wiper I02 of the finder switch I00 also grounds.

' of the selector switches S at the switching center to cause a busysignal to be transmitted to the main office if the main ofllceoperatorattempts to call the branch ofiice D .which has initiated a call to themain ofiice.

The inner right handarmature and front contact of relay I00 closes thecircuit of busy lamp I09 which may be disposed adjacent the trunk busykey I06 to prevent a repairman from cutting the trunk control equipmentout of service by operating said key when the trunk is in use.

The energization of relay I06 further closes through its inner left handarmature and front contact, a circuit for extending the main ofllcetrunk I3 through the winding of marginal relay Hi, the wiper I03 of thefinder switch and its.

' above, closes a circuit from ground through the armature of relay 0,the right hand contact thereof, and left hand outer armature and frontcontact of relay I06, the armature and back contact of relay H5 and thewinding of relay II6 to battery, whereupon relay IIO becomes energized.The energization of relay IIO closes a shunt circuit through the lefthand armature and front contact thereof and the rectifier II6 around thewinding of polar relay H0. The purpose of this shunt circuit aroundthewinding of the polar relay-which is in series relation with thetransmission circuit, is the same as the corresponding circuit describedabove in connection with the polar relay 24. However, relay 1 I0 is notbiased, and the armature thereof remains in engagement with eithercontact when the current through its operating winding is made andbroken so long as the polarity of the currentis not reversed.

The outer right hand armature and front con- I tact of relay IIO areadjusted to close before any .ofthe other contacts of said relay areclosed or broken. A circuit is thus closed initially from the winding ofrelay I00 through the outer right hand armature and front contact ofrelay I I0 and the winding of stepping. magnet I04 for holding relay I00energized. However, the current nowin: in this circuit on account of theresistance of the winding of relay I00 is not sufiicient to energize thestepping magnet I04. Upon the energization of relay II6 as described,the circuit of relay I0I.is interrupted at the right hand inner armatureand back contact'of relay IIO, whereupon the relay I0'I becomesdeenergized.

The printers I0 and 0I at the main office and branch office,respectively, are now interconnected for two-way communication throughthe wiper m ofthe finder switch 1. After the exjack I6, whereuponpositive battery is again connected to the answering trunk I0 upon thedewergization of relays 16 and I0 and the apparatus at the switchingcenter S and main ofllce M is restored to normal. Likewise the branchoffice operator may operate the marginal relay III by closing the key01, to release the finder switch I00 and restore the apparatus at-theswitching center the armature of polar relay III] to be actuated 1 intoengagement with its left hand contact, thereby opening at the right handcontact of said relay the energizing circuit of release relay 6. RelayIIB becomes deenergized and opens at its outer right hand armature andfront contact the energizing circuit of.relay I96, whereupon said relaybecomes deenergized.

The deenergization of relay I05 at its fourth right hand armaturetransfers the start circuit back to the winding of relay III'I so thatthe first finder switch will respond to the next call initiated from-onof the branch oilices. Likewise, the restoration of the second righthand armature of said relay removes ground potential from the wiper I02of the finder switch, from the winding of relay 55 and from the testcontacts in the test banks of the selector switches s. Thus the branchoifice line will no longer test busy if an attempt is made to connectthereto from one of the calling trunks I2. Relay 55 becomes deenergizedand opens at its 'left hand armature and front contact the circuit ofrelay 56, but said relay remains energized through the make-beforebreakcontacts associated with theleft hand armature of relay 55 in seriesrelation with the printer SI and relay 62 at the branch ofiice D.

The switching equipment at the switching center is thus restored tonormal when the operator at the main ofiice disconnects the printer I6from the answering trunk I3. The disconnection of the printer I6 asdescribed also disconnects the negative battery at the printer from theoperating winding of relay I6 and upon the opening of the lowerinterrupted contact I9 relay I6 becomes deremains energized through themake-beforebreak contacts associated with said armature in seriesrelation with the answering trunk I3 and the winding of relay H0 at theswitching center. In this manner, the control equipment associated withthe concentrator at the main oiiice is also restored to normal when theoperator withdraws the plug 22 from the Jack l5 as described above.

If the branch ofiice operator closes the key 61 before the main operatorrestores the switching equipment at the switching center to normal; themarginal relay II5 in series relation with the line circuit is operatedby the increased line current when the resistance 63 is short-circuited.Upon the energization of relay H5 the circuit of release relay H5 isbroken at the armature and back contact of relay H5 whereupon thecontrol quipment at the switching center associated with the finderswitch I is restored to normal in the same manner as described above inconnection with the release of the'equipment from the main oflice. Thusthe branch office is released from the connection and made available fora call from another operator at the main oflice even if the operator whohas been connected with the branch oflice fails to disconnect the mainofiice Printer promptly from the branch oflice line circuit.

In the-case of calls to or from the branch offices A and B the operationof the system is essentially the same except that the main ofiiceoperator plugs one of the printers I5 into a jack I5 individual to thewanted branch ofilce A or B and, therefore,-does not dial the number ofthe wanted oflice as in the case of a call to the branch oflicesconnected through the switching center s. The line circuits In and IIextending to the .branch oflices A and B terminate at the main oflice incontrol equipment associated with the concentrator and designated by thereference characters I20 and IZI, each of which is similar to thecontrol equipment shown in Fig. 2 asso- I21. At the end of theexchangeof business, the

main oflice control equipment is restored to normal as described abovein connection with the apparatus associated with the trunk I 3.

In order to initiate a call from one of the branch offices A or B, thebranch ofiice operator momentarily interrupts the line circuit as bypressing any key on the printer keyboard. The

interruption of the line current initiates a call to the concentratorand lights the call lamp I9 in the same manner d'secribed above inconnection with the initiation of a call over the answering trunk I3.When the main oflice operator plugs the printer I6 into the jackassociated with the lighted call lamp I9, the printer magnets andcontacts of the printers I 6 and I25 are in series relation so thattwo-way communication can'be carried on over the line circuit.

The foregoing detailed description of a system embodying the inventionis merely for the purpose of explaining the invention. The system shownand described above may be modified in various ways without departingfrom the scope of the invention. v

I claim:

1. A printing telegraph system comprising a central-station, a pluralityof branch stations,

printing telegraph equipment of the current-impulse type at saidstations, a plurality of signaling channels terminating at said centralstation, switching means remote from the central station and responsiveto current impulses for connecting certain of said channels to any ofsaid branch stations, means including the connected ones of saidchannels for controlling said switching means from the central stationwherebetween calling branch stations and the central station.

2. A printing telegraph system comprising a central station, a pluralityof branch stations,.

printing telegraph equipment at said stations, an

intermediate switching station, signaling channels between saidswitching station and each of the other stations, switching means at theswitching station for connecting central station channels to branchstation channels, means for transmitting controlling impulses over acentral station signaling channel to operate said switching means toconnect a branch station channel to said central station channel, meansfor controlling said switching means from a calling branch station toconnect the channel extending to said branch station to an idle centralstation signal-' ing channel and means operative after such connectionshave been completed at the intermediate telegrap over the same channelsemployed for setting up the connection.

3. A printing telegraph system comprising a central station, a pluralityof branch stations, printing telegraph equipment at said stations, aplurality of signaling channels terminating at said central station andcommon to each of said branch stations, means for impressing a potentialof one polarity upon a signaling channel to seize the same switchingmeans for extending said channels to the branch stations and means atthe central station to control said switching means to select a wantedbranch station, said last mentioned means including means for impressingcontrolling impulses of opposite polarity upon the seized channel.

4. -A printing telegraph system comprising a central station, aplurality of branch stations,

. printing telegraph equipment at said stations, a

plurality of signaling channels terminating at,

said central station and common to each of said branch stations,switching means for extending said channels to the'branch stations andmeans including said printing telegraph equipment at the branchstationsto control said switching means to connect a calling branch station toan idle channel to the central station.

5. A printing telegraph system comprising a central station, a pluralityof branch stations remote from said central station, printing telegraphequipment at said stations, a switching station common to said branchstations and remote from said central station and switching means atsaid switching station for connecting said central station and any ofsaid branch stations, said switching means including a polarized impulserelay responsive to impulses transmitted from the central station.

6. A "printing telegraph systemcomprising a central station, a pluralityof branch stations remote from said central station, printing telegraphequipment at said stations, a switching station common to said branchstations and remote from said central station, switching means at saidswitching station for connecting said central station and any of saidbranch stations, and means for controlling said switching means fromeither said central station or said branch stations depending upon theorigin of a call, said means for controlling the switching means fromthe central station including a polarized impulse relay arrangedtorespond to impulses of opposite polarity from the normal linepolarity.

7. A printing telegraph system comprising a central station, a pluralityof branch stations, a plurality of trunks or channels terminating atsaid central station, a source of signaling current of one polarity,means for connecting the same to said trunks or channels, switchingmeans associated with said trunks or channels and remote from saidcentral station and means for disconnecting said source of current fromthe line and for transmitting current impulses of ation for operatingthe printing ment at the connected stations any of said branch stationsthrouglisaitiitrunks orchannels.

plurality of trunks or channels terminatingat said central station,selective switchingi'means associatedwith said channels, means includingsaid switching means for interconnecting said central station and anyone of said branch's'ta'f g tions, said means including impulsetransmittin means at the central station for transmitting impulses oversaid channels, and means for rendering a printer at the central stationinoperative upon initiating a callfrom said last mentioned station untilafter said impulse-transmitting means has been operated to control theselective switching means.

9. A printing telegraph system comprising a central station, a pluralityof branch stations, a plurality of trunks or channels terminating atsaid central station, selective switching means at the other terminalsof said trunks or channels for extending said trunks or channels to anyof the branch stations, impulse-transmitting means at the centralstation for controlling said switching means, printing telegraphequipment at said central station and branch stations, and means forrendering said trunks or channels initially inoperative for thetransmission of printer signals and operative only after a predeterminedoperation of the selective switching means.

10. A printing telegraph system comprising a plurality of stations, aplurality of trunks or channels between said stations, printingtelegraph equipment at said stations, selective switching meanscontrolled over said trunks-or channels for interconnecting saidstations for operation, means for controlling said switching means oversaid trunks or channels and means for preventing the transmission ofprinter signals over said trunks or channels prior to the transmissionof impulses for controlling said switchwinding of said relay after theoperation of the selective switching means.

12. A printing telegraphsystem comprising a central station; a pluralityofbranch stations, a plurality of trunks or channels terminatingzat saidcentral station, selective switching equip- 'ment associated with eachof said channels remote from said central station for connecting any ofsaid channels with any of said branch stations and means for controllingsaid switching equipment from said centralstation, said means includingan impulsing device utilizing a potential having a polarity opposite tothat employed for normal printer operation;

13.-A printing telegraph system comprising a central station, aplurality of branch stations, a plurality of trunks or channelsterminating at said central station, printing telegraph equipment atsaid stations, selective switching equipment associated with each ofsaid channels re- ,mote from said central station, means for impressinga normal line condition upon any of said channels, means for impressingav second line condition upon said channels for communication purposes,and means for controlling said switching equipment, said last namedmeans including an impulse transmitter arranged to reverse said llneconditions and periodically interrupt said normal line condition.

14. A printing telegraph system comprising a central station, aplurality of branch stations, a plurality of trunks or channelsterminating at said central station, selective switching equipmentassociated with each of said channels remote from said central station,means for impressing upon said channels different line conditionscomprising a positive potential, a negative potential and a zeropotential, means for controlling said switching equipment from saidcentral station, said switching equipment including a relay, and meansfor rendering said relay responsive to only one of said line conditions.

15. A printing telegraph system comprising a plurality of stations,selective switching equipment for interconnecting said stations, aplurality of trunks or channels terminating at one of said stations,mains for controlling the operation of said switching equipment fromsaid one station, said means including any of said channels, means foreffecting printer communication over any of said signaling channels,means for releasing said switching equipment from said one station, saidmeans including said signaling channel and means for utilizing saidsignaling channel to provide an indication at said one station of thebusy condition at one of said branch stations to which connection hasbeen attempted. 16, A printing telegraph system comprising a centralstation, a plurality of branch stations, a plurality oi trunks orchannels terminating at said central station, switching equipmentassociated with each of said channels remote from said central station,and means including printing telegraph equipment at each of said branchstations for controlling said switching equipment from any of saidbranch stations to connect a calling branch station to saidcentral'station.

17. A printing telegraph system comprising a central station, aplurality oi. branch stations remote from said central station, aplurality of trunks or channels terminating at said central station,selective switching equipment associated with said channels forextending any one thereof to any or said remote branch stations, aplurality of branch stations having direct connection with said centralstation, printing telegraph equipment at each of said stations, andmeans for connecting the printing telegraph equipment of said centralstation alternatively for communication with any or said branchstations.

18. A printing telegraph system comprising a central station, aplurality of branch stations, a plurality of trunks or channelsterminating at said central station, selective switching equipmentassociated with each of said channels remote from said central station,said equipment including means responsive to a reversal oi the normaltrunk polarity i'or 'directively controlling and releasing saidequipment, and printer means responsive to interruptions oi the normaltrunk polarity for communicating between the central station and theconnected branch station.

19. A printing telegraph system comprising a plurality of stationsincluding a central station and branch stations remote therefrom, aplurality of trunks or channels terminating at said central station,selective switching equipment remote from said central station forextending any of said channels to any of said remote branch stations,means for controlling said switching equipment from any of saidstations, a plurality of other branch stations adjacent said centralstation, a-plurality of individual trunks or channels directlyconnecting said adjacent branch stations with said central station,printing telegraph equipment at all of said stations, and means forgrouping-all of said channels at the central station to afford thetelegraph equipment of said central station access to the telegraphequipment of direct-connected branch stations and the branch stationsconnected through said switching equipment.

20. In a printing telegraph system, a transmitting circuit, printingtelegraph equipment for transmitting and receiving printer signals oversaid circuit, a selector switch tor extending said circuit to anydesired one of a series of terminals,

- means for impressing signaling current of one polarity on said circuitand means for impressing controlling impulses of opposite polarity uponsaid circuit for stepping and releasing said selector switch whereby thetransmission of printer signals does not effect the operation of theselector switch.

21. In a printing telegraph system, printing telegraph equipment, a linecircuit, selective switching means associated with said line circuit forconnecting the same to any desired one of a series of terminals, saidselective switching means including a polarized relay connected to theline circuit, means including the printing telegraph equipment forimpressing printer sigmale of one polarity upon the line circuit, meansfor impressing controlling impulses oi opposite polarity upon the linecircuit and means including said polarized relay responsive to saidimpulses of opposite polarity for controlling the selective switchingmeans.

22. In a printing telegraph system, a plurality oi oflices, printingtelegraph equipment at said oflices, a line circuit extending from oneor said ofllces, a' selector switch associated with said circuit havinga plurality of bank contacts and a movable switch member for engagingthe same, means including said selector switch for initiating a callover said line circuit from said one 01' said ofiices to the printingtelegraph equipment at a selected one of the other offlces, means forcontrolling said selector switch including means for impressingcontrolling impulses 01' one polarity on said circuit to control thestepping of said switch by said impulses transmitted over the linecircuit and means for impressing code signalling impulses of oppositepolarity on said circuit for effecting signalling, said selector switchbeing responsive solely to said impulses oi the first-mentionedpolarity.

WILLIAM B. BLANTON.

mscLmMER 2,227,121.Willtam B. Blanton, Merrick, N. Y. PRINTING TELEGRAPHSYSTEM. Patent dated December 31, 1940. Disclaimer-filed July 3, 1943,by the assignee, The Western Union Telegraph Company.

Hereby enters this disclaimer to claims 1, 2, 3, 4, 5, 6, 7, 11, 1

of the patent,

Y [Official Gazette August 8, 1.948.]

3, 15, 16, and 1s

